Harbour: Towards Fully Onchain Multisig Operations

Signing multisig transactions typically involves exchanging transaction details and queuing them up on a centralised server before they get executed onchain. At Safe Research, we introduce Safe Harbour which moves the queue process 100% onchain. This makes signing multisig transactions more trustless and removes a central point of failure.

You can try out the prototype here.

Onchain Queues

In the EVM world today, multisig wallets like Safe are widely used to protect high value digital assets. By requiring multiple parties to approve a transaction before it executes, it introduces a layer of security that prevents any party from unilaterally moving funds.

The Safe smart contracts themselves are the gold standard to date for handling these multisig operations onchain. However, a less visible layer in the architecture lies not in the multisig smart contracts and blockchain itself, but in how multisig transactions are coordinated and queued up before reaching the chain. In Safe’s architecture for example, this service is called the transaction service.

To Pay or Not To Pay Gas

Like the Safe transaction service, many multisig wallets rely on this kind of offchain coordination layer. This is essentially a centralised service where transaction proposals are created and signatures are collected, acting as a platform to minimise gas costs by avoiding the need to execute an onchain transaction at every step of the multisig process. It’s a familiar UX vs. security tradeoff in Web3.

This offchain approach marks a clear evolution from the legacy Gnosis Multisig, which operated entirely onchain. While this offered users transparency and security, it came at the cost of a clunky UX and a gas intensive experience. No offchain database meant no flexibility in how transactions were queued, signed, or executed — making it powerful, but painful and impractical to use.

Recognising these limitations, the Safe transaction service was created. So instead of broadcasting proposals directly to the blockchain, users interact with an intermediary system where coordination is temporarily outsourced to a single, mutable, and responsive platform. This played a pivotal role for the adoption of smart contract wallets by offering a much smoother UX.

Advantages of Onchain Queues

While offchain queue coordination improves the UX significantly — by avoiding gas costs, improving privacy and reducing latency — it introduces availability and security risks:

Liveness/availability - If the offchain coordination service goes offline — due to cloud server issues, maintenance, or malicious attack — non-technical users cannot propose or sign new transactions. Even though the underlying blockchain contract is unaffected, access to funds for non-technical users (who don’t know technical alternatives) becomes practically frozen.

Verifiability - With onchain queues, it's clearly tracked who proposed a transaction, since proposals can only be submitted with a valid signature. All transaction data and approvals are stored on the blockchain, making the entire coordination process publicly verifiable and easily auditable for tampering.

A Safe Harbour Solution

Our Safe Harbour project offers an alternative to the offchain transaction service by moving pending transactions and signatures entirely onchain in the Harbour smart contract deployed to Gnosis Chain. As long as the chain is running and an RPC endpoint is available, transactions can be enqueued and executed - no additional backend or offchain indexer is required. If you do not want to use Gnosis Chain, you could deploy the Harbour contract to any other EVM chain where Safe is supported.

This approach directly tackles the Liveness/Availability of vulnerabilities of offchain coordination. Since transaction details and signatures reside onchain, no single offchain server with downtime could block transaction proposal or signing. Users can interact with the system as long as the underlying blockchain is operational. The approach also improves Verifiability, as it is clearly tracked who proposed a transaction, since you can only propose with a signature. And all data is publicly verifiable.

Our SafeHarbour project includes a web application to interact with this onchain system. This interface allows users to view pending transactions easily, append their signatures, and execute transactions once the requisite approvals are met, all while interacting directly with the onchain registry.

Try our Safe Harbour Prototype

• Play with the app here: Harbour Safe ​

  • To use the prototype:

    • Connect your Ethereum wallet (e.g., MetaMask) when prompted.

    • Enter your Safe address and select the chain.

    • View Safe configuration, pending transactions, and create or sign/execute transactions as needed.

• Check the github docs how to run it locally: docs & webapp

Note that this is an R&D prototype we are actively working on at Safe Research. It is not audited and not recommended for production grade usage.

About Safe Research

Safe Research is the applied R&D arm of Safe, dedicated to advancing the self custody stack. Our work is grounded in the cypherpunk principles of security, censorship resistance, and privacy, and we focus on building trustless, user centric infrastructure for smart accounts and wallets.

• Discuss Harbour in our forum

• Learn more about Safe Research

• Read our manifesto

Let’s make Ethereum’s original cypherpunk vision real, one commit at a time.